This invention relates to a method and apparatus for the sequential handling of a series of individual flexible products, and more particularly to a high speed handling and delivery system for flexible plastic bags or containers.
In the production of individual flexible web products such as plastic containers and bags, the bag stock is typically supplied in the form of a continuous web of thermoplastic material which has been folded upon itself to form two plies. In forming individual bags, portions of the thermoplastic material are severed from the web. These severed areas become side seams for the bags and are typically sealed at the same time as they are severed by the use of a heated wire element. The bags are then stacked, counted, and packaged by packing equipment.
The severing and sealing operation typically takes place on a relatively large diameter rotating drum which may contain multiple heated wire severing and sealing elements positioned in grooves located within the outer periphery of the drum. As the drum rotates, different severing and sealing elements are actuated to raise them up to the drum surface to sever and seal a respective portion of the bag stock web. The individual bags are retained on the drum by a vacuum arrangement as the drum rotates. Since the individual bags are formed from a continuous web, the spacing between successive bags is small, resulting from the melt back of the thermoplastic web material as the side seams are severed and sealed by the heated wire element.
Individual bags are then taken from the drum, stacked, and packaged. Desirably, the packaging operation occurs at the highest possible speed the equipment can be operated to increase productivity of the system. Further, because of the high operating speeds involved, precise timing is required for taking the bags from the product drum and transfer drum. The high operating speeds also make necessary the accurate timing of the stacking and removal of bags during their packaging.
Presently, individual bags are taken from the drum by a smaller transfer drum, also suitably equipped with vacuum capabilities. The vacuum on the bags on the large drum is relieved at an appropriate point, and the bags fall onto the smaller drum where they are held in position by vacuum. At an appropriate point, the vacuum is released and the individual bags are pulled off the smaller drum by an orbital packer or similar device.
As is conventional, the orbital packing device is provided with a set of packer fingers which move in a generally circular orbital path in timing with the smaller transfer drum so that the fingers remove successive bags, which are closely spaced and typically separated on the drum only approximately 1/8 to 1/2 inch from each other, from the drum and stack them on a stacking table against a generally vertically extending backstop. These orbiting packer fingers must move at very high speeds to strip each successive bag from the drum and may actually accelerate the bags toward the backstop. Such acceleration of the bags is undesirable as the bags may fold, bounce, or crumple when they hit the backstop. This sometimes leads to machine jams, causing excessive downtime for the machinery.
Even if the machinery does not jam, the stack of bags which is formed on the stacking table may be uneven so that when the stack is boxed, bags may be left hanging out of the box. Such boxes must be removed from the assembly line and repacked by hand. Even minor unevenness of the bag stack may make it more difficult for a consumer to dispense the bags from a box. If one or more of the bags in the stack is crumpled, the vertical height of the stack is affected so that when the count fingers are activated to separate the previous precounted stack from the next stack, the fingers may strike the stack. Again, this leads to machine jams and downtime for the machinery.
Another problem in conventional orbital packing devices is that the orbit of the packer fingers is designed so that the fingers contact substantially less than the full bag width as they move out of the grooves and strip the bag from the surface of the transfer drum. The packer fingers and their orbit are designed in this manner to prevent the fingers from contacting the leading edge of the next succeeding bag on the transfer drum as their orbit brings the fingers into and out of the grooves on the transfer drum surface. At typical operating speeds, the fingers accelerate the bags vertically downwardly away from the transfer drum surface at a high velocity. In some instances, this may cause the trailing edge of a bag, which is not in contact with the packer fingers, to fold up and over against itself. A folded bag placed on the bag stack again affects the height of the stack so that the count fingers may not operate properly to separate a predetermined number of bags from the stack. Additionally, such a folded bag may also cause a jam from the next bag striking the folded trailing edge.
A packing device having extended length packer fingers which extend and contact across substantially the full width of the bags is disclosed in commonly-assigned, copending U.S. application Ser. No. 286,205, filed Dec. 19, 1988 now U.S. Pat. No. 5,014,978. However, that application recommends that increased spacing be provided between the bags to avoid problems of the longer fingers contacting the leading edge of the next sequential bag. Increased spacing may be accomplished by increasing the surface speed of the transfer drum relative to the product drum so that bags on the transfer drum are spaced further apart. Additionally, spacing between bags may be increased by 1) employing a side-shifting transfer drum as taught in commonly assigned U.S. Pat. No. 4,911,423, issued Mar. 27,1990, or 2) a plurality of transfer drums as taught in commonly assigned U.S. Pat. No. 4,919,415, issued Apr. 24, 1990.
However, it would be desirable to be able to take advantage of the extended length fingers contacting substantially the entire surface of the bag in conventional equipment having only slight spacing of from about 1/8 to 1/2 inch between adjacent bags on the transfer drum. Further, it would be desirable to be able to control precisely the timing for the packer and count fingers and vacuum transfer mechanisms so that machine jams and stacking problems can be reduced. Accordingly, the need still exists in the art for a method and apparatus for the sequential handling and delivery of flexible products at high speeds without the folding, jamming, or stacking problems which have plagued prior art orbital packing equipment.